Delta is a new challenge for herd immunity


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A new model from James Cook University scientists shows that Australia needs to vaccinate at least 85% of the population to achieve herd immunity.

Emma McBryde, professor of epidemiology and modeling of infectious diseases at the JCU’s Australian Institute of Tropical Health and Medicine (AITHM), says modeling has implications for the federal government’s four-step plan to transition from suppression from COVID to a strategy of reopening and returning to normal life.

“The first hurdle is getting vaccinated to get it immunity, although herd immunity has become more difficult to achieve with the Delta variant, as it is more infectious and less susceptible to vaccination, ”said Professor McBryde.

He said the AITHM team is working with countries in our region to investigate and optimize herd immunity thresholds. worldwide for the original Wuhan variety and have now repeated the exercise for the Delta variant.

“We show that assuming a reproduction number (the number of people infected by someone carrying the virus) for the Delta variant of 4, we should vaccinate 85% of the Australian population using the current strategy,” said Professor McBryde .

He said if vaccine coverage was targeted at the most infectious ages, Australia could achieve immunity from the vaccinating herd 75% of the population. However, this may not be realistic, as it would require a 100% uptake in the 20-60 age groups.

“We have also shown that, even without herd immunity, vaccinated people are protected from serious illness and are much less likely to be hospitalized or die,” Professor McBryde said.

He said the AITHM team concluded that the Delta variant makes it extremely difficult to achieve herd immunity.

“But it’s important to remember that both vaccinated and unvaccinated people will have a reduced risk of infection and disease as Australia approaches . ”

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Citation: Delta, a new challenge for herd immunity (2021, July 5), retrieved July 5, 2021 at

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